PITTSBURGH, July 15 -- People with large waistlines suffer metabolic changes that significantly predispose them to developing colorectal cancer, according to new data from a University of Pittsburgh-led study whose results are published in the July 7 issue of the Journal of the National Cancer Institute. This information is the first to link intra-abdominal fat, or visceral adipose tissue (VAT), and its associated metabolic changes with colorectal cancer, according to the authors.
"For several years, scientists have recognized that obese people are more likely to develop colorectal cancer. Our study sheds light on the metabolic process underlying this connection," said Robert Schoen, M.D., assistant professor of medicine at the University of Pittsburgh School of Medicine, where he is the medical director of the Center for Families at Risk for Colorectal Cancer. "The metabolic parameters we measured, including glucose, insulin and waist circumference, reveal a risk of colorectal cancer that equals or exceeds other known risk factors, such as having a first-degree relative with this disease or consuming a high-fat or low-fiber diet."
The current report is based on a study of 5,849 people age 65 and older who participated in the Cardiovascular Health Study, a multi-center observational study of risk factors for coronary heart disease and stroke. The researchers found that people with increased waistlines, high levels of glucose (the sugar needed to fuel the body's activities) and high levels of insulin (the hormone that helps dispose of glucose) were twice as likely to develop colorectal cancer as individuals without these characteristics. Individuals in the study who developed colorectal cancer did not differ from their non-affected counterparts in terms of smoking, current aspirin use, alcoholic drinks consumed per week, percent of fat calories in diet or mean number of vegetable or fruit servings per week. Study participants were followed for an average 6.5 years.
"A very important finding here is that people with increased amounts of abdominal obesity, or VAT, do not need to be diabetic to develop colorectal cancer," remarked Lewis Kuller, M.D., Dr.P.H., chairman of the department of epidemiology at the University of Pittsburgh Graduate School of Public Health and study co-investigator. "Nondiabetics appear to have an elevated risk of colorectal cancer as their fasting insulin and glucose rise, even if glucose levels do not reach those defined as consistent with diabetes."
Previous studies have shown that insulin and insulin-like growth factors (IGFs) stimulate the growth of colorectal cancers. Obesity appears to decrease the production of proteins that bind with circulating IGFs, thus exposing the body to higher concentrations of these substances. More research is needed to clarify the roles VAT, insulin, IGF and IGF-binding factors play in causing colorectal cancer, according to the investigators.
Other researchers on the federally funded study include Catherine M. Tangen, Ph.D., department of biostatistics, University of Washington, Seattle; Gregory L. Burke, M.D., department of public health and sciences, Wake Forest University School of Medicine, Winston-Salem, N.C.; Mary Cushman, M.D., departments of medicine and pathology, University of Vermont, Burlington; Russell P. Tracy, Ph.D., departments of medicine, pathology and biochemistry, University of Vermont; Adrian Dobs, M.D., department of medicine, The Johns Hopkins University, Baltimore, Md.; and Peter J. Savage, M.D., National Heart, Lung and Blood Institute, Bethesda, Md.
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Lauren Ward
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Journal
JNCI Journal of the National Cancer Institute